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A tip of the capacitive hat

AM operators can further improve range by adding a little something to the top of the antenna called a capacitive hat.

Capacitive hats do not radiate a significant amount of signal. Instead, a capacitive hat increases the effectivness of the vertical radiator by assisting in distributing current along the full vertical length.

Without a capacitive hat, the RF current is stronger at the base of the antenna and decreases toward the top. For this reason, the upper portion of the radiator puts out very little signal.

A basic capacitive hat can be quickly made with several wires in the shape of a pyramid, supported by guy ropes. Some are made with two horizontal elements at the top of the antenna; small spokes of stiff copper tubing radiating out, with or without a perimeter wire or a hoop; or a metal disk.

A capacitive hat increases the effective height of the antenna with the beneficial side-effect of reducing the losses caused by nearby shrubs and buildings, especially where your antenna is taller than these objects.

Use at your own risk, of course, but a modest capacitive hat will not be likely be a compliance issue, there are no instances in the on line database of enforcement actions stemming from using this concept.

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